what is the purpose of Rooting a Wi-Fi Android Tablet?

I understand the purpose of rooting a phone that has 4G LTE capabilities with unlimited surfing data, so you could tether it and use internet as a separate wi-fi spot. but what is the purpose of rooting a Wi-Fi tablet?

I was going to buy a cheap tablet, as someone recommended me Dragon Touch, to root and practice messing with a tablet. but it had 2/3g capabilities of cellphone use (total of $50), but it had only 8GB. so I saw a better one for $100 and it matched my LG G Pad, since it has 16GB of data. I want to use Helium and other things that match the drive space that I could copy over and stuff > http://www.amazon.com/gp/product/B00...cUvbUpU4346140

2 questions:

1) will this 2g/3g internet be faster on my computer via Wi-Fi? or will I always be limited to 2/3g speeds after I root this Dragon Touch?

2) let's say for the sake of saying that this tablet is only Wi-Fi. so what exactly would be the purpose to root just a Wi-Fi device? I am very new new Androids and have never rooted one before. have jailbreaked an iPhone a few times, though. I am only buying this tablet to experiment with it. so if I mess it up, I won't feel bad about spending $300+ on a good tablet.